1. Field of the Invention
The invention relates generally to semiconductor memory devices, and more particularly, but without limitation, to a data strobe buffer that can be interfaced to different types of semiconductor memory devices, and a memory system including the same.
2. Description of the Related Art
Synchronous Dynamic Random Access Memory (SDRAM) devices, which operate in synchronization with the clock signal of a system, can be classified according to the class of application. For instance, Mobile Double-Data-Rate (MDDR) SDRAM devices are used in mobile devices, Double-Data-Rate (DDR) SDRAM devices are used in various devices other than mobile devices, DDR2 SDRAM and DDR3 SDRAM devices are used in applications that require operating speeds that are faster than DDR SDRAM devices, and graphics DDR (GDDR) SDRAM devices are used in graphics data processing. Each of these semiconductor memory device types has different properties and may thus require different types of memory controllers. For example, DDR SDRAM devices may use a memory controller having a single-ended type data strobe buffer which compares the data strobe signal with the reference voltage, whereas DDR2 SDRAM devices may use a memory controller having a differential type data strobe buffer which compares the data strobe signal with the inverted signal of the data strobe signal.
Therefore, a data strobe buffer which can enable the memory controllers of different types of semiconductor memory devices is needed.